Severe combined immunodeficient (SCID) mice are amenable to transplantation with various human tissues and have proven to be valuable tools with which to study HIV pathogenesis, anti-viral efficacy, gene therapy, immunologic development and opportunistic pathogens. The objective of this proposal is to develop a core facility for the breeding, maintenance and reconstitution of SCID mice for experimental use by investigators of the UAB CFAR. The specific aims of the core reflect this objective and are as follows: 1. To provide high-quality pathogen-free SCID mice to UAB CFAR investigators; 2. To provide specially-designed, centrally located BSL 2/3 animals space so that infectious HIV research can be physically restricted to specific areas; 3. To construct hu-PBL SCID mice and limited numbers of SCID-hu (Thy/Liv) for HIV related research; 4. To provide ongoing training, supervision, and monitoring of investigators and their research staff regarding BSL-2/3 practices required for HIV research; 5. To provide expertise on the construction and manipulation of mouse human chimeras and to provide high cost equipment on a shared basis within the core facility in order to facilitate and broaden the research capabilities of all investigators and to avoid redundancy in equipment purchases; 6. To development new mouse/human chimeric models for HIV related research; 7. To foster the development of HIV/AIDS research by new investigators and to encourage multidisciplinary research by new and established investigators.